1. Field of the Invention
This invention relates to electoluminescent materials and in particular to infrared emmissive materials. This material can be fabricated as a thin film which may be used as an efficient source of infrared radiation or in special display applications.
2. Description of the Prior Art
Electroluminescent compositions produce characteristic emission upon application of a voltage across the layer or thin film of the composition with current passing through the layer or film. Such compositions typically have produced visible emission and have found use in flat panel displays. A more recent application of electroluminescent compositions are in thin film devices of the edge emitter type where the emitted light is directed out of the edge of the thin film as a light source.
A well known thin film electroluminescent material is zinc sulfide containing manganese dopant in an amount of from about 0.1 mol percent to about 4 mol percent. This well known material has been used in thin film electroluminescent {TFEL} displays as seen in U.S. Pat. No. 4,006,383, and more recently in edge emitting optical radiation sources as seen in U.S. Pat. No. 4,535,341.
The prior art zinc sulfide doped with manganese exhibits a characteristic emission with a broad band centered at 590 nanometers and extending from about 530 to 640 nanometers when the thin film is subject to a drive voltage across the film.
In certain applications for thin film edge emitter light sources it is desired to produce infrared emission. This is because in many printer applications an infrared laser is currently used to actuate infrared sensitive photoreceptors, which are particularly sensitive at about 780 nanometers in the infrared.